Abstract：
Demography of herbivorous mammal populations may be affected by changes in predation, population density, harvesting, and climate. Whereas numerous studies have focused on the effect of single environmental variables on individual demographic processes, attempts to integrate the consequences of several environmental variables on numerous functional traits and demographic rates are rare. Over a 32-year period, we examined how forage availability (vegetation assessed through NDVI) and population density affected the functional traits and demographic rates of a population of Columbian ground squirrels (Urocitellus columbianus), a herbivorous hibernating rodent. We focused on mean population phenology, body mass, breeding success, and survival. We found a negative effect of population density on demographic rates, including on breeding success and pup and adult survival to the next year. We found diverging effects of vegetation phenology on demographic rates: positive effects of a later start of the growing season on adult and yearling female survival, and juvenile survival, but no clear effect on male survival. Interestingly, neither population density nor vegetation affected population phenology or body condition in the following year. Vegetative growth rate had a positive influence on female mass gain (somatic investment) over a season, but both vegetative growth rate and biomass, surprisingly, had negative effects on the survival of young through their first hibernation. Thus, ground squirrels appeared to benefit more from later timing of vegetation than increases in vegetative biomass per se. Our study provides evidence for complex ecological effects of vegetation and population density on functional traits and demographic rates of small mammal populations.
摘要：
食草哺乳动物种群的人口可能会受到捕食变化的影响，人口密度，收获,和气候。尽管许多研究都集中在单个环境变量对个体人口统计过程的影响上，尝试整合几个环境变量对许多功能特征和人口统计学的影响很少。在32年的时间里，我们研究了牧草的可用性（通过NDVI评估的植被）和种群密度如何影响哥伦比亚地松鼠（Urocitelluscolumbianus）种群的功能特征和人口比率，一种食草的冬眠啮齿动物。我们关注的是平均人口物候,体重,繁殖成功,和生存。我们发现人口密度对人口比率有负面影响，包括繁殖成功以及幼崽和成虫存活到明年。我们发现植被物候对人口统计学的不同影响：生长季节的后期开始对成年和一岁雌性存活的积极影响，和青少年生存，但对男性生存没有明显影响.有趣的是,人口密度和植被都不会影响第二年的人口物候或身体状况。植物生长速率对一个季节的女性体重增长（体细胞投资）有积极影响，但是营养生长速度和生物量，令人惊讶的是,通过第一次冬眠对年轻人的生存产生了负面影响。因此，地松鼠似乎比植被本身的增加受益更多。我们的研究为植被和种群密度对小型哺乳动物种群的功能特征和人口统计学率的复杂生态影响提供了证据。
